Fan stopped on Inspiron 600m

Hi all I was carrying my laptop and I bumped the front left corner on a wall. After that I noticed that the fan wasn't on. After poking, prodding, and knocking around the surface it came back on (think of that scene from Zoolander..."the files are IN the computer??") After that, everytime I checked to hear if the fan was running for the next couple days, it was, then today it stopped again. Poke & prod and after about 20 minutes it came on again. I don't know if I'm actually doing anything when I mess around with it, or if simply the fan isn't on all the time and I'm just now noticing when its not? I guess the only straight question I can think of asking is if the fan is supposed to be on all the time? Has this happened to anyone else/ have you been able to fix it? I'd hate to fry my computer by getting to comfortable and not noticing the fan not on... Any advice is greatly appreciated Thank you, Katie